Since many sigs have a lot of large images that take a lot of unnecessary space, you may have onle ONE image in your signature, with a reasonable size, in effect now. It's ridiculous to read though a page of posts where 95% of the page is just images.
Edit: You can have more than one picture, if they are side by side in your signature.
Edit 2: Make sure the image(s) don't take more than 1/2 of space on your screen, otherwise reduce them in size. Images of excessive size will be removed because they simply take too much space (and for many people with dial-up connections, take a lot of time to load.)